Fukushima Watch: Are the Oi Reactors as Safe from Earthquakes as the Government Says?

By Yoko Masuda

The two nuclear reactors Japan is preparing to restart weren’t vetted for safety as thoroughly as they should have been — at least from the standpoint of earthquake safety, two prominent seismologists say.

European Pressphoto Agency

Katsuhiko Ishibashi, seismologist and professor at Kobe University, speaks in Tokyo on June 26.

Katsuhiko Ishibashi, a seismologist and professor emeritus at Kobe University, and Mitsuhisa Watanabe, a tectonic geomorphologist and professor at Toyo University, took the podium Tuesday to talk about the potential perils at the Oi nuclear plant, which the government has approved for restart, as well as the pitfalls in reactor safety assessments right now.

The government’s assessment of the safety of the Wakasa Bay region, where the Oi plant is located, is based on the assumption that there are two active underwater faults in the area, and that the nuclear plants have taken all necessary measures to withstand a quake, if one was to occur.

Mr. Ishibashi argues, however, that the government has underestimated the power of the ground movements that the faults in the area will produce. At Tuesday’s talk, to a group of foreign reporters in Tokyo, he also said there could be a third active fault nearby. If all three faults move simultaneously, Mr. Ishibashi said, that could mean more shaking than the government has anticipated.

What’s more, the three faults in the area around Oi could be connected, said Mr. Watanabe. “You cannot deny the evidence that there could be a chain reaction on that line,” he said. That would significantly raise the possibility of greater shaking in the area.

Why do these researchers have such a different view of the faults and their dangers than the government?

In answer, Mr. Watanabe points to an example of another disputed fault, named F-6, located under the Oi plant. Kansai Electric had two geological diagrams of the structure of the fault, which it had created and submitted to nuclear regulators in the 1980s when it first applied for a permit to build reactors there. The diagram of the southeast side of the fault didn’t show anything, but the one of the northwest side suggested possible activity, Mr. Watanabe said. Yet Kansai Electric submitted only the diagram of the southeast side to regulator Nuclear and Industrial Safety Agency when it went through its recent assessment of whether the fault was active, Mr. Watanabe said.

“The expertise and neutrality of the ‘experts’ (who evaluated the plant) are highly questionable,” said Mr. Watanabe. The government should have done more research before ordering the Oi reactors restarted, he said. Both men said the government and utilities should get outside independent experts to check the seismic safety of nuclear plants.

A spokesman for Kansai Electric confirmed the utility had submitted only the southeast diagram, but said it had no intention of hiding the other. The company had submitted the diagram “as one example to show the results of the construction permit,” the spokesman told JRT. Furthermore, Kansai Electric had reexamined its data in 2010, under new government safety guidelines, and has concluded that the fault has been inactive for 120,000 to 130,000 years, he said.

A NISA spokesman said the regulator couldn’t get more recent diagrams of the fault because the area now has buildings constructed over it. NISA is still looking into the matter, he told JRT, asking Kansai Electric for original photographs from when the diagrams were first created. Kansai Electric says the photographs have been lost, but NISA is asking them to check again, he said.

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